lavu/hmac: Add support for SHA-2

Includes HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512.
Tested using test vectors from https://tools.ietf.org/html/rfc4231

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
fate: Add test vectors for HMAC SHA and SHA-2

Also replace custom tests for MD5 with those published in RFC 2202

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>